Automotive exhaust component and method of manufacture

ABSTRACT

A catalytic converter for an internal combustion engine exhaust system comprises a single-piece, seamless metal housing having tubulated gas inlet and outlet ports and a tubulated intermediate section with a catalytic element therein. The intermediate section is connected to the inlet port by an inlet transition section and to the outlet port by an outlet transition section. The inlet and outlet ports and the inlet and outlet transition sections are formed by swaging the ends of a seamless tube used to form the housing. Exhaust gas produced by operation of the engine passes into the converter and through the catalytic element. Noxious substances in the exhaust, including CO, NO x , and incompletely combusted hydrocarbons are converted to more benign substances through the action of the catalytic element, which is preferably a frangible ceramic honeycomb structure having a plurality of internal passages coated with a catalytically active substance. A swaging process is used to form tubulated ends on the converter. The tabulated ends minimize production of turbulence in the gas flow and allow the converter to be connected to the rest of the exhaust system by clamped, welded, or flanged joints. The one-piece, seamless construction of the converter is economical to produce and eliminates welding of housing components that tend to fail when subjected to corrosive exhaust gasses over a prolonged period of time.

This application claims the benefit of provisional application No.60/367,419, filed Mar. 26, 2002.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the field of automotive exhaust components;and more particularly, to a muffler, catalytic converter or the like,that is formed and housed within a seamless enclosure.

2. Description of the Prior Art

It is widely recognized that the exhaust emissions of internalcombustion engines constitute a major source of air pollution throughoutthe world. The combustion process in these engines inevitably results inthe production of certain substances that pass into the exhaust streamand are detrimental to the health and well being of humans and otheranimal and plant species. The emissions of concern include particulates(soot) along with gases such as CO, SO₂, NO_(x), and imperfectly burnedhydrocarbons (HC). These substances are produced in the combustionprocess, along with the CO₂ and H₂O that are the products of thecomplete oxidation of the hydrocarbons comprised in fuel.

The combination of market forces and governmental environmentalregulations has spurred research and development of ways to mitigate oreliminate the production of the harmful constituents in engine exhaust.Automakers and suppliers have been challenged to control and reducevehicle tailpipe emissions by the U.S. Clean Air Act of 1965 andsubsequent legislation in the U.S. and other countries. In response tothis legislation, virtually every system in the engine has beenimproved. As a result, modern engines more efficiently convert thelatent chemical energy in fuels to useful mechanical work, so that theiremissions are markedly reduced.

To date the significant efforts have been directed toward thefour-stroke Otto engine in passenger automobiles, owing to consumerpreferences and government action. Despite progress in emissionreduction for these automobile engines, increasingly stringent limitshave been imposed. Emission regulations have also extended to otheron-road vehicles, such as busses, and trucks, many of which employdiesel engines; to off-road vehicles; and to non-propulsion engines,many of which are two-stroke.

Much of the improved emissions stem from use of catalytic convertersthrough which exhaust gas streams are directed. The passage of theexhaust across a surface comprising a suitable catalyst promotes furtherchemical reaction that removes a substantial fraction of the noxious CO,NO_(x), and HC substances, converting them instead into more benignsubstances such as CO₂, O₂, N₂, and H₂O. Moreover, use of catalyticconverters in combination with computer-driven, adaptive control oftiming and fuel-air mixture gives an engine designer significantflexibility when optimizing engine-operating parameters to achievereduced emissions.

Notwithstanding the market pull coming from the significant advantagesrealized by interposition of catalytic converters in the exhaust streamthere remain substantial impediments to their manufacture. It would bedesirable if converters could be manufactured using reliable, efficientand inexpensive construction processes; maintained durability andfunctionality over a prolonged service life. However, conventionalconverters fail to afford these desirable characteristics.

Converter constructions must produce a gas-tight enclosure so thatexhaust enters solely at an inlet port and exists exclusively through anoutlet port. Failure to achieve a hermetic sealing deleteriously allowsleakage of exhaust gas, circumventing the beneficial effect of thecatalyst and producing unacceptable noise. In some cases, leakage ofexhaust containing combustible gases can lead to engine backfiring anddamage to other portions of the engine system. Leakage can also exposevehicle occupants to unhealthy or dangerous levels of CO and otheremissions. In addition, leaks have been known to trigger catastrophicvehicle fires.

Understandably, automobile manufacturers are impelled by several factorsto minimize or eliminate these catalytic converter failures. Thereputation of a manufacturer as a supplier of a high-quality product isdegraded by reported failures. In addition, both market forces andcurrent U.S. environmental regulations compel an auto manufacturer towarranty the integrity and efficacy of all aspects of an auto'spollution control system. More specifically, the regulations requirethat the system function to maintain the auto's emissions withinestablished standards for an extended period of time and mileage. Anyfailures expose the manufacturer to costly warranty repairs and to theire of an inconvenienced consumer.

Heretofore, the metal housings used for catalytic converters have mostlyfallen into three broad categories of construction: a “pancake” or“clamshell” form, a wrapped form, and a multipiece form, each of whichencloses a catalytic substrate bearing catalytically active material.

Typically, the “pancake” or “clamshell” form comprises stamped upper andlower shells, which are substantially identical to each other, and whichhave mating, peripheral, side flanges that are welded together to lie ina plane containing the longitudinal axis of the housing. They are shapedto form an internal chamber in which the catalytic substrate is mountedby “L-shaped” or other known brackets or pre-formed features providedintegrally in the housing component shells.

The wrapped-form housing is made with material that initially issheet-like and formed so as to generally encircle the catalyticsubstrate. This form is also known as a “tourniquet wrap,” reflectingits construction. The edges of the housing must be joined at a weldedseam that runs essentially the full axial length of the converter. Theinlet and outlet ports in this construction may either be formed as partof the wrapping operation or, more commonly, may comprise separatecomponents welded to the ends of the housing subsequent to the formationof the sheet material.

Several multipiece housing constructions are known. One form disclosedby U.S. Pat. No. 5,118,476, comprises a tubular middle section in whichthe catalytic substrate is placed and end bushings attached to each endof the middle section. U.S. Pat. No. 6,001,314 discloses a two-piecehousing. Each of the pieces is shaped by deep drawing to provide an openend and a conical outer end tapered to an opening appointed forconnection to associated exhaust system pipes. The two pieces are weldedtogether with the catalytic substrate contained within.

Each of these multi-piece constructions must be sealed by welding,either to close a seam in a sheet-like material or to affix appropriateend caps. The welding is needed both to provide the required hermeticsealing of the housing and to secure the catalytic substrate. However,each of these welds is a likely failure mode. Moreover, the OBD2(on-board diagnostics) standard mandated by the U.S. EnvironmentalProtection Agency for passenger vehicles after 1996 imposes a furtherneed for hermetic integrity in the engine exhaust system. This standardmandates measurement of O₂ content before and after the catalyticconverter as a required input for the computerized engine controlsystem. Even a pinhole leak in the system between the sensorscompromises the accuracy of the comparison in O₂ levels which is usedfor a mass balance determination. The emissions control system fails,negating the ability of the engine control system to adaptively optimizetiming and fuel/air mixture to minimize emissions. Such failure of theemissions control system must be corrected under warrantee by thevehicle manufacturer at considerable expense and inconvenience to theconsumer.

The environment of a catalytic converter is harsh for a multiplicity ofreasons, each of which can potentially cause penetrating corrosion andultimate failure of the converter housing. For example, a converter usedin an on-road vehicle, especially in cold climates, is exposedexternally to a spray of road salt and internally to acidic exhaustgases. It is well known in the art that chemical and stress effectscombine to make weldments especially likely loci of corrosive attack.Accordingly, a catalytic converter housing that could be formedefficiently and economically into a single piece without welding haslong been sought in the automotive art. Such a one-piece catalyticconverter housing would overcome serious shortcomings involving thereliability of extant multi-piece and welded housing forms.

The only known technique for producing single-piece housings isspinning. In this process, a catalytic element is placed within a tubeand the combined workpieces are rapidly spun about the tube'scylindrical axis while suitable tools are brought into contact with thetube at each of its ends. Sufficient deformation is thus accomplished toform tubular ports of reduced diameter at each end of the tube.Depending on the required reduction, the spinning may be carried outeither cold or hot. While the spinning approach does produce asingle-piece housing, it also carries substantial drawbacks. Theproduction forming is expensive and energy-intensive to conduct.Moreover, it results in formation of circumferential ridges on both theinside and outside surfaces of the housing in the deformed region. Theseridges are both unattractive and present significant disruption of thegas flow inside the muffler, causing turbulence and undesirable backpressure that reduce the engine power available for a given cylinderdisplacement. The magnitude of diameter reduction achievable by spinningis limited. In addition, substantial work hardening is produced in themetal in the reduced section. As a result, the ductility of the tube inthe reduced section, including the port tubulation, is too low to allowthe converter to be attached to adjoining exhaust sections by ordinaryclamps. Welded or flanged joints must be used instead. The need forwelding joints is particularly inconvenient for aftermarket and repairuse.

The spinning process is further limited by the size and shape of productthat it can produce. Very long shapes are unwieldy to secure and spin atthe required rate in available lathes and similar machine tools.Moreover devices produced by spinning must be rotationally symmetricabout a cylindrical axis, or the resulting imbalance makes it impossibleto spin the device and accomplish the needed forming of the desiredshape. In many cases the circuitous path available for the exhaustsystem would make it highly desirable to have non-symmetric componentsavailable, such as a catalytic converter in which the inlet and outletports need not be coaxially aligned, but angulated or offset relative toone another. Such configurations cannot be formed by known spinningmethods. Furthermore, areas of the housing formed by spinning arework-hardened to an extent that renders subsequent bending and likeoperations virtually impossible.

As a result of these deficiencies, spinning is not widely used in themanufacture of exhaust components, notwithstanding the eagerness of themarket for a viable single-piece, seamless device which spinning mightbe thought capable of producing.

SUMMARY OF THE INVENTION

The present invention provides a catalytic converter for an internalcombustion engine exhaust system having a single-piece, seamlessmetallic housing, and a method for constructing the converter. Thecatalytic converter comprises: (i) a tubulated gas inlet port in thehousing through which exhaust gas is introduced; (ii) a tubulated gasoutlet port in the housing through which the exhaust gas is discharged;(iii) a tubulated intermediate section of the housing having an inletend and an outlet end; (iv) an inlet transition section connecting theinlet port and the inlet end of said intermediate section; (v) an outlettransition section connecting the outlet end of the intermediate sectionand the outlet port; and (vi) a catalytic element contained within theintermediate section and through which the exhaust gas passes whenflowing between the gas inlet port and the gas outlet port. The interiorsurfaces of the inlet and outlet transition sections and the gas inletand outlet ports are smooth and substantially free from ridges thereon.The inlet and outlet ports and the inlet and outlet transition sectionsare formed by swaging the ends of a seamless tube used to form thehousing.

Exhaust gas produced by operation of the engine passes into theconverter and through the catalytic element. Noxious substances in theexhaust, including CO, NO_(x), and incompletely combusted hydrocarbonsare converted to more benign substances through the action of thecatalytic element, which preferably comprises a frangible ceramichoneycomb structure having a plurality of internal passages coated witha catalytically active substances.

Advantageously, the one-piece, seamless converter construction of theinvention is economical to produce and eliminates welding of housingcomponents that are highly prone to failure. More specifically, theone-piece, seamless construction of the converter housing reduces thesize and number converter parts (as compared with known practicalconstructions) while, at the same time, increasing the converter'seffectiveness and improving its construction and manufacture. Theconverter is inherently economical to produce and can bemass-manufactured in the large volumes required to supply originalequipment converters directly to manufacturers of automobiles and trucksfor factory installation in exhaust systems. Furthermore, theimprovement of the housing affords additional advantages includingbetter vehicle fuel efficiency and better manufacturing economics.

The elimination of any welding of seams or end caps afforded by theone-piece construction of the present catalytic converter greatlyenhances its reliability during service. Welds are notoriouslyvulnerable as loci of corrosive attack due both to chemical and stresseffects. In operation, catalytic converters in typical on-road vehicleapplications are exposed externally to road salt and other corrosivesubstances and internally to acidic exhaust gases. The absence ofweldments in the present catalytic converter removes a prime source offailures during the service life of the device.

The manufacture of the catalytic converter of the invention comprisesuse of swaging processes to form the tubulated ends of the catalyticconverter. The central section of the housing, being generally larger ininner dimension than the ends, envelops and holds the catalytic elementin position. Swaging is used in the practice of this invention generallyto reduce the ends of the housing to a tube diameter appointed forconnection of the converter to the adjoining components of the engineexhaust system.

Compared to other known methods used to form ends, swaging affords anumber of advantages. The reduction in diameter can be carried out in asequence of steps using a plurality of dies. As a result, the swagingprocess is highly adaptable, providing a designer with great flexibilityin tailoring a housing to fit into an available space and in optimizingthe dynamics of gas flow through the device. The tubulated ends andtransition sections are smooth and substantially free of circumferentialridges on either the inside or outside surfaces. The external appearanceof the device is enhanced. The smoothness of the inside surface and theabsence of ridges thereon minimizes generation of turbulence thatimpedes the flow of exhaust gas through the converter and causesexcessive backpressure. Swaging maintains a level of ductilitysufficient to allow the converter to be connected to the rest of theexhaust system by clamped, welded, or flanged joints.

A further advantage of the present method over spinning is its abilityto form more intricate structures, including those having features suchas extended length and bends or other non-symmetrical configuration.Since the present end-forming process does not entail rapid rotation ofthe workpiece, neither balance nor the size of available lathes orsimilar machine tools is a consideration. Structures need not have acylindrical axis of rotational symmetry. End-forming can thus produceconverters having inlet and outlet ports which are angulated or offsetrelative to one another. A converter could also be formed with bends inany of its sections. Designs can also be formed wherein the catalyticelement is an oval cylinder instead of a right circular cylinder.

In one aspect of the invention the catalytic element comprises afrangible ceramic honeycomb structure having a plurality of passagesextending therethrough. The surfaces of the passages are substantiallycovered with a finely dispersed, catalytically active substance. Thisconstruction makes effective use of the catalytic substance, whichgenerally comprises one or more of the expensive platinum-group noblemetals including Pd, Pt, and Rh. The ceramic honeycomb is preferablyencircled with a mat of an intumescent material which acts toresiliently and insulatively secure it within the inside diameter of theintermediate section. The intumescence of the mat material creates areliable and gas-tight seal that protects the ceramic during itsconstruction and in-service life. In addition, the intumescent materialforces the exhaust gas stream to pass through the passages of thehoneycomb, maximizing catalytic efficacy.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood and further advantages willbecome apparent when reference is had to the following detaileddescription of the preferred embodiments of the invention and theaccompanying drawings, wherein like reference numerals denote similarelements throughout the several views and in which:

FIG. 1 is a perspective view of a catalytic converter in accordance withthe invention;

FIG. 2 is a longitudinal, cross-sectional view along the axial mid-planeof the catalytic converter depicted by FIG. 1;

FIG. 3 is a longitudinal, cross-sectional view along the axial mid-planeof a catalytic converter in accordance with another aspect of theinvention; and

FIG. 4 is an axial cross-sectional view taken in the intermediatesection of the converter depicted by FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is directed to a catalytic converter, muffler,pre-catalytic converter, or the like, incorporated in the exhaust systemof an internal combustion engine. Generally stated, the catalyticconverter is housed in a single-piece, seamless metallic housingpreferably made of a corrosion-resistant metal alloy such as a stainlesssteel alloy. The housing has tubulated gas inlet and outlet portsthrough which exhaust gas is introduced and discharged, respectively.The converter also comprises a catalyst element contained within atubulated intermediate section of the housing. During its passagethrough the converter, exhaust gas is caused to flow over the surface ofthe catalyst element. A catalytically active material present on thecatalyst element promotes chemical reactions that purify the gas stream.This is accomplished by converting certain chemical species therein toother species which are generally considered not harmful to life or theenvironment, or which present a significantly reduced danger.

Referring now to FIGS. 1 and 2 there is shown generally at 10 acatalytic converter comprising one aspect of the invention. Thecatalytic converter 10 has a one-piece, seamless metal housing composedof a corrosion-resistant metal, preferably stainless steel. Theembodiment depicted by FIG. 1 is generally cylindrical, having a roundcross-section at each point along its axial length. Housing 12 isgenerally tubular in shape, and is provided with tubulated gas inletport 14 having inlet orifice 16 and tubulated gas outlet port 18 havingoutlet orifice 20. Converter 10 is appointed for use in the exhaustsystem of an internal combustion engine (not shown). Inlet port 14 isconnected to tubulated intermediate section 22 of housing 12 by inlettransition section 24. Intermediate section 22 is connected to outletport 18 through outlet transition section 26. Exhaust gas producedduring operation of the internal combustion engine enters the converterthrough inlet orifice 16 in inlet port 14. The exhaust gas then passessuccessively through inlet transition section 24, intermediate section22, and outlet transition section 26, before being discharged throughoutlet orifice 20 of outlet port 18. Inlet and outlet ports 14, 18 ofconverter 10, though of reduced diameter owing to the manufacturingprocess described hereinafter, are not work hardened. As a result, theports, 14, 18 of converter 10 can be readily connected to othercomponents of the exhaust to produce welded, clamped, and flanged jointsby suitable means known in the engine art.

The arrangement of the components inside the catalytic converter 10 ofFIG. 1 is best seen in the cross-sectional view of FIG. 2. Converter 10further comprises catalytic element 28. In an aspect of the inventioncatalytic element 28 comprises a generally cylindrical, frangible,heat-resistant ceramic honeycomb substrate 30 having a large number ofpassages 32 thereto, each of the passages 32 running generally parallelto the cylindrical axes of both substrate 30 and intermediate section22. Passages 32 are generally arranged in a honeycomb pattern or asimilar array. Passages 32 extend completely through substrate 30,thereby allowing the passage of gas from one end 34 of element 28 to theother end 36 thereof. In an aspect of the invention substrate 30 iscomposed of cordierite. Other ceramic materials having adequatestrength, thermal shock resistance, heat resistance, and chemicalcompatibility both with the exhaust gas stream and catalyst materialapplied thereto may also be used. The interior surfaces of passages 32are substantially covered with a substance catalytically active toinduce the chemical reaction of substances present in engine exhaust forthe purification thereof. In some aspects of the invention, catalyticelement 28 may comprise a plurality of ceramic or other substratesarranged sequentially or in parallel, e.g. to achieve better gas flow,to provide more than one type of catalyst, or to facilitate manufactureof a longer converter. Sequentially disposed substrates may be insubstantially abutting relationship or may be separated by a free spacewhich may be desired for optimizing gas flow.

One skilled in the art will also appreciate that while the aspect shownin FIGS. 1 and 2 is cylindrically symmetric, the invention alsocontemplates aspects in which bends, angulations, and othernon-symmetric features may be present. The intermediate section may beoval or “pancake” shaped and have a catalyst element of mating shapetherein. In addition, the inlet and outlet ends may be extended to serveas portions of the engine exhaust system. While this extension entailsadditional forming steps, the corresponding reduction in the number ofparts in the total engine exhaust system is advantageous both forsimplifying assembly and for eliminating otherwise required joints thatare also prone to corrosion failure.

The present catalytic converter may advantageously employ a variety ofknown catalytically active substances. Many of these substances containnoble metals such as Pt, Pd, and Rh. As a result of the needs to (i) usethese high cost materials as efficiently as possible and (ii) maximizethe catalytic surface's effective area, the catalyst material isgenerally provided in a finely divided form coated on, and adhered to, acatalytic substrate. Suitable catalyst materials include three-waycatalysts appointed to convert nitrous oxides, carbon monoxide, andhydrocarbons to nitrogen, water, and carbon dioxide. Means for selectinga suitable catalyst material and for ascertaining the specific activityand the effective surface area of a catalytic material are well known inthe catalyst art. The converter may also comprise an oxidation catalystand means (not shown) for supplying secondary air to intermediatesection 22 so as to promote conversion of carbon monoxide andhydrocarbons to water and carbon dioxide. Other forms of catalystsubstrate, including metallic catalyst support systems, may also be usedin the practice of the present invention.

Ceramic substrate 30 is preferably supported and held securely insealing contact within intermediate section 22 by a generally encirclingmat 38. The mat is preferably resilient, insulative, and shock absorbentand may be composed of a gas impervious, vermiculite based material,available in the open market. The material is intumescent, that is, itexpands substantially upon heating. Typically a mat having an initialthickness of approximately ¼″ is used. During assembly of converter 10,mat 38 is wrapped to substantially encircle the ceramic substrate 30 andcover at least a portion of its longitudinal or axial length.Preferably, a short portion of the cylindrical periphery of the ceramicsubstrate 30 at each of its ends 34, 36 is left uncovered by mat, asdepicted by FIG. 2. Preferably, the axial length uncovered at each endranges from about half to three times the thickness of the mat. Thisholdback ensures that portions of the mat do not break off and block anyof the passages through honeycomb structure 30. The wrapped mat 38 iscompressed radially to a thickness approximately half of its initialthickness prior to insertion of the combined substrate 30 and mat 38into the inner diameter of intermediate section 22 to secure thepositioning of the combined assembly within the converter housing 12.

One form of mat suitable for the practice of the invention comprises aflexible intumescent sheet, which may be used for mounting automotivecatalytic converter monoliths. The sheet comprises an unexpandedvermiculite produced by subjecting vermiculite ore containinginterlamellar cations to a potassium nitrate solution for a timeinterval sufficient to ion-exchange interlamellar cations within the orewith potassium ions; an inorganic fibrous material; and a binder. Thesheet material may be provided with, or temporarily laminated to, abacking sheet of kraft paper, plastic film, non-woven synthetic fiberweb, or the like. Another suitable form of intumescent sealing mat 38 isavailable on the market under the trade name of “3M INTERAM MAT.”Suitable intumescent sealing mat is also sold commercially by Unifrax astype “XPE.”

Advantageously the intumescence of mat 38 ensures the secure mounting ofcatalytic substrate 30 within the converter housing. In addition, theintumescent mat 38 seals the gap between the outside cylindrical surfaceof catalytic substrate 30 and the inside cylindrical surface ofintermediate section 22. This “sealing action” forces substantially allthe gas flowing into the converter 10 through inlet port 16 to passthrough internal passages 32 in substrate 30 before exiting throughoutlet port 18. Efficacy of the catalytic material coating the surfaceof internal passages 32 is thereby enhanced, since exhaust gas ismaximally exposed thereto. The resiliency of mat 38 serves to cushionand protect frangible substrate 30 during the initial fabrication ofconverter 10. Moreover, mat 38 retains this resiliency even afterrepeated thermal cycling. The constituents of converter 10 experiencedifferential thermal expansion and contraction during each cycle ofheatup, operation, and cool-down of the engine wherein exhaust passesthrough converter 10. By virtue of maintaining its resiliency, mat 38 isable to protect substrate 30 from damage due to this pattern ofdifferential expansion, while still maintaining an adequate degree ofsealing during the entirety of each operating cycle.

While the aspect of the invention depicted by FIG. 1 comprises acatalytic converter employing a catalyst dispersed and supported on aceramic substrate, other forms of catalyst and substrate may also beused in the practice of the invention. For example, a catalyst may bedispersed on a metallic substrate, which may take the form of corrugatedmetal foil that is coiled upon itself to form a generally cylindricalstructure having a plurality of passages longitudinally extendingtherethrough. Since metals are substantially less frangible and tougherthan known ceramic catalyst substrates, a metal catalytic support ofthis form may allow elimination of intumescent material 38 in theconstruction of converter 10.

A variety of metallic alloys are suitable for the housing of theinvention. Alloy selection is made on the basis of cost and the level ofperformance required with respect to temperature capability, durability,and corrosion resistance needed. For automotive use, ferritic stainlesssteels are commonly used, including various 400-series alloys. Mostcommonly 409SS and SAE51409 alloys are employed. For small engines,including non-propulsion applications, and other instances where costconsiderations are dominant, carbon steels are frequently used. Fordemanding applications wherein especially long life and high corrosionresistance are desired, such as marine engines, austenitic and300-series stainless steel alloys such as 304SS are generally employed.

The catalytic converter of the invention may be manufactured in a widerange of sizes to accommodate the requirements of different engines,which may range from small engines of a few horsepower or less, such asmight be used in lawn mowers, snow blowers, weed trimmers, and similaroff-road, non-propulsion applications, to large diesel engines used intrucks. Many present automotive applications employ ceramic substratescommercially available in standard diameters of 2.5 and 4 inches.Automotive converters are typically about 9 to 20 inches in totallength. Small, non-propulsion engines may employ substrates as small as1 inch diameter or even less and may be only a few inches long. Theminimum length of the substrate is generally determined by the flowvelocity and the amount of time the exhaust gas must be at the catalyticsurface to achieve a chemical reaction that sufficiently reduces theconcentration of pollutants. The total length of the converter is thendetermined both by the length of the active catalyst and the requiredshaping of the transition sections and the inlet and outlet ports. Oftenthe inlet and outlet ports of a converter are approximately half thediameter of the substrate to reduce exhaust flow impedance. The taperingof the inlet transition and outlet transition sections may range fromvery gradual to very abrupt. For automotive applications the transitionsections are often chosen with a straight taper of 10–15° forsimplicity. However, curved transitions are generally advantageous forbetter aerodynamics. In one aspect of the invention, the intermediatesection is cylindrical and the length of the inlet and outlet transitionsections is chosen so that each length ranges from about 30% to 100% ofthe diameter of the intermediate section.

The catalytic converter shown in FIGS. 1–2 and described hereinabove isof the so-called under-floor type normally disposed under the floor ofan automotive vehicle for reasons of available space. However, it willbe understood by one skilled in the art that the principle of thepresent invention may be applied to catalytic converters of manydifferent types, including those types appointed to be mounted proximatethe exhaust manifold of an internal combustion engine. These types aresometimes denoted as pre-cat catalytic converters if mounted withinabout thirty-six inches of the manifold or as pre-light catalyticconverters if mounted within about eight inches of the manifold.Additionally, it will be appreciated that the principle of the presentinvention may be applied to the manufacture of catalytic converters fora variety of internal combustion engines other than those of anautomotive vehicle, and converters that are integrated with mufflers,resonators, or other similar components in the exhaust system.

In accordance with the invention, the inlet and outlet transitionsections and the inlet and outlet ports of the catalytic converter areformed by swaging. In the aspect of the invention depicted in FIGS. 1–2,the converter housing 12 is formed from a cylindrical metallic tube, thediameter of which is uniform through its length. The ends of the tubeare swaged to form the transition sections 24, 26 and the ports 14, 18with mat 38 and substrate 30 being located in intermediate section 22.As depicted by FIG. 2, the inside diameter of intermediate section 22through substantially its entire length is d_(t). A swaging operationforms transition section 24 and inlet port 14, tapering the tubesmoothly to a diameter of d_(i) in the inlet port region, so that inletport 14 may be attached to the preceding component of the exhaustsystem. A swaging operation is also used to form outlet transitionsection 26 and outlet port 18. The diameter d_(o) of outlet port 18 maybe the same as diameter d_(i) of inlet port 14. Alternatively, differentdiameters may be selected to accommodate the requirements of the exhaustsystem.

In FIGS. 3 and 4 there is shown an aspect of the invention comprising avariation of the form of the housing 12 depicted by FIGS. 1 and 2. Inthis aspect, further swaging is optionally applied to intermediatesection 22 of housing 12 to form therein a plurality of rib-likeindentations 50, which are axially elongated along intermediate section22. Preferably indentations 50 extend along a substantial portion ofintermediate section but do not extend to inlet and outlet transitionsections 24, 26. The cross-sectional view of FIG. 4, taken at lines A—Ashown by FIG. 3, depicts an aspect in which three such indentations arepresent. Preferably indentations 50 extend radially inward to a depth ofat most half the thickness of intumescent mat 38. They act to furthersupport and constrain mat 38 and substrate 30 from axial movement and toassure sealing of the mat/substrate assembly within the walls of housing12. Indentations 50 should not be so deep as to cause fracture ofsubstrate 30.

FIG. 3 also depicts optional circumferentially-extending indentations 52at the junction between inlet transition section 24 and intermediatesection 22 and at the junction between intermediate section 22 andoutlet transition section 26. These indentations 52 serve to support andconstrain substrate 30 from moving axially. If present, theseindentations are preferably of a depth less than or about equal to thethickness of the mat. This indentation in some cases also advantageouslyimproves the uniformity of gas flow across presented at the face area ofsubstrate 30. In other embodiments a screen, baffle, or similarstructure may also be used to protect the inlet and outlet of theceramic substrate from the intrusion of foreign matter and to improvegas flow.

The swaging used to form each of the ends of converter housing 12 iscarried out by mechanically forcing a die over each end of the tube, theforce being applied in a generally axial direction and the die beingdesigned to cause flow of the metal and thereby reduce the tube'sdiameter while maintaining its circularity. Preferably, the swaging iscarried out in a plurality of swaging steps using a plurality of dies toform each end of the converter housing 12. A suitable sequence of diesmay further be used to achieve a desired profile in the transitionsection. The profile may be as simple as a cone, but preferablycomprises a more complicated pattern having a combination of curvaturesin which there is no discontinuity in the slope of the inside surface ofthe converter in its axial direction. In one aspect of the inventionboth ends of the housing are swaged simultaneously by applyingoppositely directed compressive forces to dies on each end usinghydraulically driven rams.

The flexibility in choosing the profile of the transition sections ofthe present converter is highly advantageous. The profile ischaracterized, in part, by the curvature at each point along the lengthof the transition sections and the overall rapidity with which thesections taper. A converter designer must satisfy several constraints.The overall length of the converter may be limited to a maximum lengthby available space. The required gas flow rate, allowable impedance togas flow, and required extent of exposure of the exhaust to activecatalyst, along with available forms of substrate and the geometry ofthe passages therethrough, generally constrain the area and lengthrequired for the catalytic element. In addition, properly designedtransition sections advantageously maintain a generally laminar flow ofexhaust gas and minimize the generation of unwanted turbulence therein.This turbulence undesirably increases the impedance of the catalyticconverter and results in excessive back pressure. The absence of theabove-mentioned discontinuity in slope in the transition sections,together with suitable transition profiles with gradually tapereddiameters, minimizes this turbulence.

A further advantage of swaging over other forming techniques, such asspinning, is its ability to produce reduced sections while maintainingsmoothness of both the interior and exterior surfaces of the converter.When properly carried out, significant reductions in diameter can bemade without producing internal and external circumferential ridges thatare typically produced by spinning.

Advantageously the swaging technique results in an exterior surface thatis smooth and aesthetically appealing, minimizing its vulnerability topitting, corrosion, or like attack, and rendering it easily finishableby plating or other coating operations. The swaging technique alsoproduces a smooth inner surface without significant ridges. If present,such ridges on the interior surface of an exhaust component are afurther source of undesirable turbulence, as previously discussed.

A further disadvantage of techniques such as spinning is the amount ofwork hardening that results in the reduced section. This work hardeningis highly detrimental in that it leaves the inlet and outlet ports witha ductility level that is insufficient to allow the ports to be reliablyand hermetically attached to other exhaust components by clamping.Instead, joints have to be made using welds or flanges, which are moreexpensive and difficult to implement, especially with after-marketinstallations.

In an aspect of the method of the invention the forming process iscarried out semicontinuously. Seamless tubes having substantially thediameters desired for the intermediate section are supplied in longlengths. From these tubes are cut preforms adapted to be formed into thecatalytic converter housing. Ceramic substrates are provided having thedesired diameter and length. Each substrate is wrapped with anintumescent mat to form the catalytic element. The mat is compressed andthe combined assembly inserted into the free end of the supply tube. Thesupply tube is then gripped circumferentially and its free end is swagedto form the inlet port and inlet transition section. Subsequently, thesupply tube is cut to remove a portion thereof having a requisitepreselected length, thereby defining the preform. The preform is thenre-gripped and the other end swaged to form the outlet port and outlettransition section. Most of the steps of this process are easilyautomated to provide a high level of manufacturing efficiency andprocess control, thereby minimizing production costs.

In another aspect of the method of the invention, performs are cut tolength from a seamless tube having substantially the diameter desiredfor the intermediate section of the converter. A ceramic substrateshaving the requisite length is wrapped with an intumescent mat to formthe catalytic element and inserted approximately in the middle of eachpreform. The preform is then placed in a hydraulic ram assembly havingswaging dies coaxially aligned and adapted to be forced compressivelyover each of the preform's ends, thereby simultaneously swaging eachend. A plurality of dies are sequenced into a hydraulic ram and usedstepwise to accomplish the desired reduction to the final inlet andoutlet port diameters and to form the inlet and outlet transitionsections. Alternatively, a plurality of rams are used, with the preformbeing indexed between rams, which are appointed with a desired sequenceof dies to progressively swage the ends in a plurality of graduatedswaging stages.

The following example is presented to provide a more completeunderstanding of the invention. The specific techniques, conditions,materials, proportions and reported data set forth to illustrate theprinciples and practice of the invention are exemplary and should not beconstrued as limiting the scope of the invention.

EXAMPLE 1 Preparation and Testing of a Catalytic Converter

A catalytic converter of a type commonly used for emissions reductionfrom an automobile engine was formed using a catalytic elementcomprising a conventional platinum-group noble metal type of catalystsupported on the walls of multiple passages extending through acordierite ceramic honeycomb structure. The honeycomb structure wasabout 3.6 inches in diameter and 3 inches long. The housing for theconverter was formed from a seamless tube of 409 stainless steel alloyhaving an outside diameter of about four inches and 0.049 inch walls.The honeycomb structure was wrapped with an intumescent mat compressedto about 0.12 inches thickness, and the combined mat and ceramic werethen inserted into the center part of the generally tubular converterhousing. The ends of the housing were then end-formed to provide aninlet port section and an outlet port section, each of which having adiameter of two inches and a length of two inches. Tapered transitionsections about two inches long joined the inlet and outlet sections tothe central section.

The converter was subjected to standard tests known in the automotiveindustry and conformed to procedures set forth in 40 CFR 85.2116. Thefollowing tests were conducted.

The expansion of the intumescent mat material was tested by a dial-gagetechnique. The mat was heated to a maximum temperature of 825° C. andits expansion was measured and found to exhibit a maximum of about120–130% relative to its initial thickness. This value is well withinthe usual range known in the art to result in satisfactory sealing andpositioning of a ceramic substrate in a catalytic converter housing.

The cold push-out resistance of the ceramic substrate was measured by astandard mechanical pressing technique. The experiment was carried outby gripping the converter housing and exerting mechanical force throughan arbor pressing axially on the substrate. It was found that a force ofabout 60–80 pounds was required to initiate shear of the intumescent matand cause displacement of substrate. The observed force was well withinstandards recognized in the art, in which movement at less than about 30pounds indicates an inadequately supported and sealed substrate, whilemovement at over about 200 pounds is indicative of excessive engagementof the substrate by the intumescent mat that is likely to result inchipping or brittle failure of the substrate during converter use.

The catalytic efficiency of the converter was measured by a sweep testusing gas chromatographic analysis of the conversion efficiency forknown CO, HC, and NO_(x) pollutants to benign substances. Minimalback-pressure was observed, confirming the adequacy of flow through theconverter, including the catalytic substrate. Satisfactory catalyticefficiency performance was observed, indicating the suitability of theconverter for use in an automotive application that achieves compliancewith applicable emissions standards.

The results of the foregoing tests establish that a one-piece, seamlessconverter satisfactorily demonstrates performance sufficient to meetrequirements for emissions mitigation in an automotive application.

Having thus described the invention in rather full detail, it will beunderstood that such detail need not be strictly adhered to but thatvarious changes and modifications may suggest themselves to one skilledin the art, all falling within the scope of the present invention asdefined by the subjoined claims.

1. A catalytic converter for an internal combustion engine exhaust system, comprising the converter having interior and exterior surfaces and: a. a single-piece, seamless metallic housing; b. a tubulated gas inlet port in said housing through which exhaust gas is introduced; c. a tubulated gas outlet port in said housing through which the exhaust gas is discharged; d. a tubulated intermediate section of said housing having an inlet end and an outlet end, said intermediate section having a plurality of rib-like indentations which are axially elongated along said intermediate section; e. an inlet transition section connecting said inlet port and said inlet end of said intermediate section; f. an outlet transition section connecting said outlet end of said intermediate section and said outlet port; and g. a catalytic element contained within said intermediate section and through which said exhaust gas passes when flowing between said gas inlet port and said gas outlet port; the interior surfaces of said intermediate section said inlet and outlet transition sections and said gas inlet and outlet ports having been swaged and being smooth and substantially ridge-free.
 2. A catalytic converter as recited by claim 1, wherein said catalytic element comprises: a. a ceramic substrate having a plurality of passages extending therethrough; and b. a catalytically active material present on a substantial portion of the surface of each of said passages.
 3. A catalytic converter as recited by claim 2, further comprising an intumescent mat encircling said ceramic substrate and sealing the external surface of said ceramic substrate to the inner surface of said intermediate section.
 4. A catalytic converter as recited by claim 1, wherein each of said catalytic element and said intermediate section has a length, and said length of said catalytic element is at least about 80% of the length of said intermediate section.
 5. A catalytic converter as recited by claim 1, wherein said intermediate section is substantially cylindrical and has diameter, each of said inlet and outlet transition sections has a length, and said length of each of said inlet and outlet transition sections ranges from about 30% to 100% of said diameter of said intermediate section.
 6. A catalytic converter as recited by claim 5, wherein: a. said catalytic element comprises a ceramic substrate having a diameter, a plurality of passages extending therethrough, and a catalytically active material present on a substantial portion of the surface of each of said passages; and b. said inlet port has an inlet diameter and said outlet port has an outlet diameter, and said inlet and outlet diameters are approximately one half of said diameter of said substrate.
 7. A catalytic converter as recited by claim 1, wherein said metallic housing is composed of a stainless steel alloy.
 8. A catalytic converter as recited by claim 1, wherein said exterior surface of said catalytic converter is smooth.
 9. A catalytic converter as recited by claim 1, wherein said rib-like indentations extend along a substantial portion of said intermediate section.
 10. An internal combustion engine system having an exhaust system comprising a catalytic converter, said catalytic converter comprising: a. a single-piece, seamless metallic housing; b. a tubulated gas inlet port in said housing through which exhaust gas is introduced; c. a tubulated gas outlet port in said housing through which the exhaust gas is discharged; d. a tubulated intermediate section of said housing having an inlet end and an outlet end, said intermediate section having a plurality of rib-like indentations which are axially elongated along said intermediate section; e. an inlet transition section connecting said inlet port and said inlet end of said intermediate section; f. an outlet transition section connecting said outlet end of said intermediate section and said outlet port; and g. a catalytic element contained within said intermediate section and through which said exhaust gas passes when flowing between said gas inlet port and said gas outlet port; the interior surfaces of said intermediate section said inlet and outlet transition sections and said gas inlet and outlet ports having been swaged and being smooth and substantially ridge-free.
 11. A catalytic converter for an internal combustion engine exhaust system, comprising: a. a single-piece, seamless metallic housing; b. a tubulated gas inlet port in said housing through which exhaust gas is introduced; c. a tubulated gas outlet port in said housing through which the exhaust gas is discharged; d. a tubulated intermediate section of said housing connecting said gas inlet port and said gas outlet port, said intermediate section having a plurality of rib-like indentations which are axially elongated along said intermediate section; e. an inlet transition section connecting said inlet port and said inlet end of said intermediate section; f. an outlet transition section connecting said outlet end of said intermediate section and said outlet port; and g. a catalytic element contained within said intermediate section and through which said exhaust gas passes when flowing between said gas inlet port and said gas outlet port; the interior surfaces of said intermedicate section said inlet and outlet transition sections and said gas inlet and outlet ports having been swaged being smooth and substantially ridge-free; said catalytic converter having been produced by a process comprising: i. providing a seamless metallic tube having a first end and a second end; ii. inserting said catalytic element in said tube; iii. gripping said tube; iv. swaging said first end to form said gas inlet port and said inlet transition section; and v. swaging said second end to form said gas outlet port and said outlet transition section; and vi. swaging said intermediate section to a reduced diameter.
 12. A catalytic converter as recited by claim 11, wherein said swaging is carried out using a plurality of swaging steps. 